But that test you did is the same as taking a picture of a horse, then one of an elephant and then another of a dog. They are completely different????
Also, the first one is underexposed a fair bit, the second a little bit and the third is about right. If you had used f4 and 1/50 for all three then they would all be exposed correctly for the chair. You would have blown out the sky in the first obviously but you were exposing for the chair were you not? It's the only thing in the three pics so I presume you were.
Take the footballer example again. When you are at a game what are you trying to expose correctly? The footballer.
OK, so what is lighting the footballer? The floodlights.
So, like your example above, he decides to stand in the one spot for a few minutes and you decide you would like a few different shots of him at different focal lengths. So you find out what are the exposure settings required to expose the footballer correctly. You use your 300mm lens to spot meter off his chest as he is wearing a middle grey shirt

The meter results are 1/640 at f2.8 and ISO1000.
You look through the viewfinder and notice that your camera is indicating that it will underexpose by 1/3 of a stop at the settings you are using but you take a shot of him in manual mode at 300mm and BINGO, you have a head shot and it's exposed bang on. The camera indicated it would underexpose because of the darkness beind him.
OK. So you now decide that you'd like a full length shot as well so you switch to your 135 lens. You put in the same settings and you look through the viewfinder and notice that this time your camera is indicating that it will underexpose by 2/3 of a stop at the settings you are using but you take a shot of him in manual mode at 135mm and BINGO, you have a full length shot and the footballer is exposed bang on. The camera indicated it would underexpose because there was more darkness behind him in the stands.
So finally you now decide that you'd like a wide angle shot as well so you switch to your 24mm lens. You put in the same settings and you look through the viewfinder and notice that this time your camera is indicating that it will underexpose by 1 & 2/3 of a stop at the settings you are using but you take a shot of him in manual mode at 24mm and BINGO, you have a wide angle shot and the footballer is exposed bang on. The camera indicated it would underexpose because there was more darkness behind him in the stands and the dark sky. The crowd isn't exposed correctly because you didn't want them exposed correctly but the footballer so the same settings were correct.
Now if you were to use Av or Tv or whatever Nikon use like your example of the giraffe, dog amd antelope above then you would of course get completely different values if you used evaluative metering but if you were to use spot metering on the footballer then you WILL get the exact same exposure values and if your camera doesn't give you the same values then there is something wrong with it. Must be because its a Nikon